1. Field of the Invention
The present invention relates to a projection color image display apparatus such as a liquid crystal projector, and more particularly, to a projection color image display apparatus of a single panel type that uses only one optical modulating device such as a liquid crystal display device.
2. Description of the Related Art
Liquid crystal display apparatuses include a direct-view display apparatus, and a projection display apparatus (what is called a liquid crystal projector) for projecting and displaying an image on a screen. In general, the liquid crystal projector directs lights of primary colors for color display, which are color-separated from light radiated from a single white light source, to pixels (liquid crystal cells) of a liquid crystal display device respectively corresponding to the colors, modulates the lights according to reproduction image signals, and projects the lights onto a screen, thereby displaying a color image. Such color liquid crystal projectors are roughly divided into two types: a single-panel type using a single liquid crystal display device provided with a color separation means for separating light into three colors, red (=R), green (=G), and blue (=B), and a three-panel type using three monochrome liquid crystal panels respectively provided for red, green and blue optical paths.
The single-panel color liquid crystal projector generally employs a color filter as a color separation means. Conventionally, the color filter is integrally formed with a liquid crystal display device.
FIG. 7 illustrates a conventional single-panel color liquid crystal projector using such a color-filter-combined liquid crystal display device (hereinafter referred to as a CF-combined liquid crystal display device). In the liquid crystal projector, white light emitted from a source lamp 101 enters an ultraviolet and infrared cutting filter 102, where ultraviolet and infrared rays are absorbed, and then, enters a condenser lens 103. The light condensed by the condenser lens 103 is radiated onto a CF-combined liquid crystal display device 104 located in the rear of the condenser lens 103. When passing through a liquid crystal layer (not shown) of the CF-combined liquid crystal device 104, the white light is modulated according to image signals applied to pixel electrodes on the CF-combined liquid crystal display device 104 provided for each of the primary colors (R, G and B). The white light is also color-separated into a R light, a G light, and a B light by a color filter 104a that is integrally formed with the CF-combined liquid crystal display device 104, transmitted through the CF-combined liquid crystal display device 104, and then, emitted. These modulated colored lights are condensed and synthesized by a projection lens 105 located in the rear of the CF-combined liquid crystal display device 104, and projected onto a screen 106 in an increased size.
In the projection color image display apparatus having such a structure, the aforesaid color filter 104a in the CF-combined liquid crystal display device 104 is generally made of organic pigment. Since the color filter of this pigment type absorbs light with a specific wavelength from incident light and transmits light with other wavelengths, the absorbed light is turned into heat and generates heat, or near ultraviolet rays, which are not cut by the ultraviolet-infrared cutting filter, are absorbed. Such heat generation or absorption deteriorates the color filter itself, and also affects other constituents. In particular, since the color filter using organic pigment originally has low resistance to weather, it is prone to fade with use, and color quality of a display image is thereby degenerated. Accordingly, it is an important problem to restrict this heat generation or absorption, particularly in light of future trends toward higher brightness.
Moreover, the color filter using organic pigment shows a gentle spectral transmittance curve, and has a characteristic of transmitting therethrough lights with a wide range of wavelengths other than the specific wavelength. Therefore, the use of the color filter of this type lowers color purity of a formed image.